1. Field of the Invention
The present invention relates to an optical transmission apparatus, and particularly to an optical ring system using a wavelength-division multiplexing technology and the structure of a node for optical communication used in the optical ring system.
2. Description of Related Art
A prior art of an optical transmission apparatus having a ring structure in which a plurality of nodes are connected in the form of a ring is described with reference to FIGS. 1 and 2. The prior art is described in detail in a paper entitled xe2x80x9cHighly Reliable and Economical WDM Ring with Optical Self-Healing and 1:N Wavelength Protectionxe2x80x9d by Uehara et al., printed in the Conference Publication (published in 1997) of the 11th International Conference on Integrated Optics and Optical Fiber Communications, 23rd European Conference on Optical Communications.
FIG. 1 shows the configuration of an optical transmission apparatus according to a first prior art. An optical transmission apparatus shown in FIG. 1 has been implemented by combination of a wavelength-multiplexed optical transmission technology and a 4-fiber-ring transmission apparatus. FIG. 1 shows an example of an optical ring system using m nodes. Each of the nodes included in the system multiplexes optical signals having wavelengths of xcex1 to xcexn and transmits them as a wavelength-division-multiplexed optical signal.
The optical transmission apparatus shown in FIG. 1 is composed of optical add/drop multiplexing nodes 301-1 to 301-m, transmission path optical fibers 302-1 to 302-4 (302-1: counterclockwise working system, 302-2: clockwise working system, 302-3: counterclockwise protection system, and 302-4: clockwise protection system), an optical preamplifier 351, a wavelength demultiplexer 352, a wavelength multiplexer 353, an optical booster amplifier 354, an optical preamplifier 355, a wavelength demultiplexer 356, a wavelength multiplexer 357, an optical booster amplifier 358, an optical preamplifier 359, a wavelength demultiplexer 360, a wavelength multiplexer 361, an optical booster amplifier 362, an optical preamplifier 363, a wavelength demultiplexer 364, a wavelength multiplexer 365, an optical booster amplifier 366, an add/drop multiplexers (ADM) 367-1 to 367-n, and transponders (TRPD) 371 to 378 each regeneratively repeating by converting a received optical signal into an electrical signal and converting again it into an optical signal.
In FIG. 1, the m nodes are connected with one another in the form of a ring by a total of four transmission path optical fibers two of which connect bi-directionally the working system and the other two of which connect bi-directionally the protection system. Each of the nodes sends out an optical signal obtained by multiplexing n wavelengths of xcex1 to xcexn in wavelength division to each of the four optical fiber transmission paths. And each of the nodes receives an optical signal obtained by multiplexing n wavelengths of xcex1 to xcexn in wavelength division from each of the four optical fiber transmission paths.
Next, operation in each of the nodes of an optical transmission apparatus of a former ring structure having the above-mentioned structure is described in the following.
An optical signal received from a transmission path optical fiber of the counterclockwise working system is amplified by the optical preamplifier 351 and is demultiplexed by the wavelength demultiplexer 352 into n wavelength components of xcex1 to xcexn. Hereupon, the n optical signals of xcex1 to xcexn obtained by wavelength-demultiplexing are respectively inputted into the add/drop multiplexers (ADM) 367-1 to 367-n. That is to say, an optical signal of xcex1 is inputted into the ADM 367-1, an optical signal of xcex2 is inputted into the ADM 367-2, and an optical signal of xcexn is inputted into the ADM 367-n. And n optical signals of xcex1 to xcexn in wavelength are outputted from the ADM""s 367-1 to 367-n. Through the transponders 371 to 378, an optical signal of xcex1 in wavelength is outputted from the ADM 367-1, an optical signal of xcex2 in wavelength is outputted from the ADM 367-2, and an optical signal of xcexn in wavelength is outputted from the ADM 367-n. The n optical signals of xcex1 to xcexn in wavelength outputted from the ADM""s 367-1 to 367-n are multiplexed in wavelength division by the wavelength multiplexer 353. Optical output of the wavelength multiplexer 353 is amplified by the optical booster amplifier 354 and then is sent out to the optical fiber transmission path of the counterclockwise working system. Also with regard to optical signals transmitted and received through the other transmission paths, namely, the clockwise working system 302-2, counterclockwise protection system 302-3 and clockwise protection system 302-4, the multiplexing and demultiplexing operations of wavelengths of xcex1 to xcexn are performed in the same way as the above-mentioned operation. In FIG. 1, the optical preamplifier 355, the wavelength demultiplexer 356, the wavelength multiplexer 357 and the optical booster amplifier 358 are applied to the clockwise working system, the optical preamplifier 359, the wavelength demultiplexer 360, the wavelength multiplexer 361 and the optical booster amplifier 362 are applied to the counterclockwise protection system, and the optical preamplifier 363, the wavelength demultiplexer 364, the wavelength multiplexer 365 and the optical booster amplifier 366 are applied to the clockwise protection system.
Operation in the ADM 367-1 is as follows.
Each of the four optical signals of xcex1 in wavelength inputted by the wavelength demultiplexers 352, 356, 360 and 364 is processed by an optical/electrical (O/E) conversion, an overhead signal termination and a time-division demultiplexing process in a high-speed signal reception interface part (HSRx), and then is inputted into a cross-connecting part (TSA) as an electrical data signal. And the electrical data signals are each inputted from the cross-connecting part (TSA) into the high-speed signal transmission interface part (HSTx), and are each processed by a time-division multiplexing process, an overhead signal insertion and an electrical/optical (E/O) conversion, and then an optical signal of xcex1 in wavelength is outputted to the wavelength multiplexers 353, 357, 361 and 365. A cross-connecting part (TSI) has a function of selectively connecting four pairs of electrical data signals inputted from the high-speed signal reception interface part (HSRx) and four pairs of electrical data signals to be outputted to the high-speed signal transmission interface part (HSTx) according to a state of breakage of a transmission path and the like in the ring network, and a function of disconnecting or connecting a part or the whole of an inputted electrical data signal from or with a low-speed signal interface part (LS) and inserting a signal from the low-speed signal interface part (LS) into an output signal.
This optical ring system, in case that a transmission path breaks down, changes over an optical signal being transmitted in the working system transmission path to a transmission path of the protection system by changing over the path in the cross connection part (TSI) by an electrical switch and thereby recovers the transmission path from the breakdown. That is to say, in case that break of an optical transmission path of the working system has occurred, the switch of the cross-connecting part (TSI) in each ADM operates to change over an optical signal transmission path from the working system to the protection system.
Communication through the protection system optical transmission path performed by the first prior art is called Standby-Line-Access, and makes possible two kinds of communication using the working system and the protection system in case that no failure occurs on the optical transmission path. It is a matter of course that since communication through the protection system optical transmission path is changed over to communication through the working system in case of a failure of break of the transmission path, communication through the protection system during an ordinary working period becomes impossible in case of failure.
Next, a ring-shaped optical transmission apparatus according to a second prior art is described as follows. FIG. 2 shows an example of an optical ring structure using m nodes, and each of the nodes multiplexes optical signals having wavelengths of xcex1 to xcexn in wavelength division and transmits them as a wavelength-division-multiplexed optical signal.
The optical transmission apparatus shown in FIG. 2 is composed of optical add/drop multiplexers 401-1 to 401-m, transmission path optical fibers 402-1 to 402-4 (402-1: counterclockwise working system, 402-2: clockwise working system, 402-3: counterclockwise protection system, and 402-4: clockwise protection system), an optical preamplifier 451, a wavelength demultiplexer 452, a wavelength multiplexer 454, an optical booster amplifier 455, an optical preamplifier 456, a wavelength demultiplexer 457, a wavelength multiplexer 458, an optical booster amplifier 459, an optical preamplifier 460, an optical booster amplifier 461, an optical preamplifier 462, an optical booster amplifier, 463, an 8xc3x978 optical matrix switch 470 having 8 inputs and 8 outputs, an 8xc3x978 optical matrix switch 471, a 4xc3x974 optical matrix switch 480 and a 4xc3x974 optical matrix switch 481.
The optical transmission apparatus of FIG. 2 according to the second prior art introduces the 4xc3x974 optical switches 480 and 481 as a recovery measure against break of an optical transmission path and the like. By this, the second prior art reduces to about half the scale of the electrical switches/HSTx/HSRx in the optical add/drop multiplexer shown in the first prior art and reduces the cost of a node in comparison with the optical transmission apparatus of FIG. 1 according to the first prior art.
The optical transmission apparatuses according to the above-mentioned prior arts have problems as shown in the following.
First, the optical ring system according to the first prior art converts every input optical signal into an electrical signal regardless of whether it should be dropped or not. Therefore, although an inputted optical signal requiring no conversion to an electrical signal and no reconversion to an optical signal is included in inputted signals, an add/drop multiplexer (ADM) for processing a data signal of 1 wavelength in each node requires four high-speed signal transmission/reception interface parts for all the transmission paths and cross-connecting circuits for route-changing all signals connected with these high-speed signal transmission/reception interface parts. Accordingly, there has been a problem that an optical ring system of n wavelengths requires the devices n times this case and results in becoming very expensive and large-scale.
And the optical ring system according to the second prior art aims at making small-sized/economical apparatus by integrating switches each required for each path into a 4xc3x974 optical switch in order to solve the problem of the first prior art. However, since an optical transmission path of the protection system is dedicated to protection of the working system, there is a problem that communication using an optical transmission path of the protection system, the communication being performed in the first prior art, becomes impossible. That is to say, since communication is performed only by the working system in the second prior art, the circuit utilizing efficiency of the ring is low.
An object of the present invention is to provide a wavelength-division multiplexing optical transmission apparatus having a simple structure and further having highly reliable nodes for optical communication and a ring structure composed of the same nodes.
An optical communication node according to the present invention comprises a plurality of optical switches each having at least one optical input terminal and at least one optical output terminal, wherein an optical signal from the outside is inputted to the at least one optical input terminal, and each of the at least one optical input terminal and each of the at least one optical output terminal are selectively connected with each other.
This optical communication node is provided with at least one wavelength demultiplexer for demultiplexing a wavelength-multiplexed light inputted into the optical communication node into the respective wavelength signal lights and inputting each of the wavelength signal lights into each of the at least one optical input terminal, and at least one optical signal merging device for merging and sending out a plurality of optical signals outputted from a part of the at least one optical output terminal to a single output transmission path.
The wavelength demultiplexer and the optical coupler contained in the optical communication node each comprise an arrayed waveguide grating (AWG).
A first optical communication node according to the present invention comprises a first optical switch in which the plurality of optical transmission paths to be connected to first input and output terminals are connected respectively to its plurality of input terminals and which selectively connects each of the plurality of input terminals and each of the plurality of output terminals to each other, a second optical switch in which the plurality of optical transmission paths to be connected to second input and output terminals are connected respectively to its plurality of output terminals and which selectively connects each of the plurality of input terminals and each of the plurality of output terminals to each other, a first to an Mth (M is a natural number, and hereinafter the same) wavelength demultiplexer in each of which its input terminal is connected with the plurality of output terminals of the first optical switch and the plurality of output terminals of the second optical switch and each of which demultiplexes an inputted wavelength-multiplexed optical signal into optical signals of the respective wavelengths, a first to an Nth (N is a natural number, hereinafter the same) optical coupler in each of which its output terminal is connected with the plurality of input terminals of the first optical switch and the plurality of input terminals of the second optical switch and each of which couples and sends out plural inputted optical signals to a single output transmission path, and a third optical switch in which the output terminals of the first to Mth wavelength demultiplexers are connected with its input ports and the input terminals of the first to Nth optical couplers are connected with its output ports and which selectively connects each of the input ports and each of the output ports to each other.
A second optical communication node according to the present invention comprises a first to a fourth wavelength demultiplexer, a first to a fourth optical coupler, a first optical switch in which the input terminals of the first and second wavelength demultiplexers are respectively connected with its first and third output ports, the second working optical path is connected with its second output port, the second protection optical path is connected with its fourth output port, the output terminals of the first and second optical couplers are respectively connected with its second and fourth input ports, the first working optical path is connected with its first input port, and the first protection optical path is connected with its third input port, a second optical switch in which the input terminals of the third and fourth wavelength demultiplexers are respectively connected with its second and fourth output ports, the first working optical path is connected with its first output port, the first protection optical path is connected with its third output port, the output terminals of the third and fourth optical couplers are respectively connected with its first and third input ports, the second working optical path is connected with its second input port, and the second protection optical path is connected with its fourth input port, and a third optical switch in which the output terminals of the first to fourth wavelength demultiplexers are connected with its input ports and the input terminals of the first to fourth optical couplers are connected with its output ports.
The third optical switch contained in the second optical communication node is provided with a plurality of 2-input optical switches in which the first input ports are connected with the output terminals of the first to fourth wavelength demultiplexers and the first output ports are connected with the input terminals of the first to fourth optical couplers, and which selectively outputs an optical signal inputted through an input port from one of the output ports according to a selection signal applied from the outside.
The second optical communication node further comprises a first to an eighth transponder each having a function for converting once each of optical signals inputted from plural input terminals into an electrical signal and converting them again into optical signals and outputting them through plural output terminals, the first to fourth transponders being respectively inserted between the first to fourth wavelength demultiplexers and the third optical switch, and the fifth to eighth transponders being respectively inserted between the first to fourth optical couplers and the third optical switch.
The third optical switch is provided with a plurality of 2-input optical switches in which the first input ports are respectively connected with the plural output terminals of the first to fourth transponders, the first output ports are respectively connected with the plural input terminals of the fifth to eight transponders, and which selectively output an optical signal inputted through an input port from one of the output ports according to a selection signal applied from the outside.
The transponder comprises an optical receiver which converts an optical signal inputted from each of the plural input terminals into a reception electrical signal of an electrical signal and outputs it, an optical state monitoring circuit which detects a state of the optical signal by monitoring the reception electrical signal and outputs it as a monitor signal, and an optical transmitting circuit which converts the reception electrical signal into a transmission optical signal and outputs it to the plural output terminals.
The second communication node further comprises a receiving circuit in which its reception signal input terminal is connected with the second output ports of some 2-input optical switches out of the plural 2-input optical switches and which converts a reception optical signal inputted through the reception signal input terminal into an electrical signal, and a transmitting circuit in which its transmission signal output terminal is connected with the second input ports of some 2-input optical switches out of the plural 2-input optical switches and which converts an electrical signal into an optical signal and outputs the transmission optical signal through the transmission signal output terminal.
And the second optical communication node further comprises a fourth optical switch in which its input ports are connected with the second output ports of the plural 2-input optical switches and its output ports are connected with the second input ports of the plural 2-input optical switches, a receiving means in which its reception signal input terminal is connected with the output ports of the fourth optical switch and which converts a reception optical signal inputted through the reception signal input terminal into an electrical signal, and a transmitting means in which its transmission signal output terminal is connected with the input ports of the fourth optical switch and which converts an electrical signal into an optical signal and outputs the transmission optical signal through the transmission signal output terminal.
Each of the first to fourth wavelength demultiplexers and the first to fourth optical couplers contained in the second optical communication node comprises an arrayed waveguide grating.
Each of the first to fourth optical couplers of the second optical communication node comprises an optical tree coupler.
The second optical communication node further comprises at least one first optical amplifier inserted between two connection points of the first working optical path and the optical communication node, at least one second optical amplifier inserted between two connection points of the second working optical path and the optical communication node, at least one third optical amplifier inserted between two connection points of the first protection optical path and the optical communication node, and at least one fourth optical amplifier inserted between two connection points of the second protection optical path and the optical communication node.
Each of these first to fourth optical amplifiers is provided with an optical fiber amplifier or a semiconductor optical amplifier.
An optical transmission apparatus according to the present invention is an optical transmission apparatus in which plural optical communication nodes are connected in the form of a ring through a first and a second working system optical transmission path and a first and a second protection system optical transmission path, and which transmits a wavelength-multiplexed optical signal, the optical transmission apparatus comprising a first to a fourth wavelength demultiplexer, a first to a fourth optical coupler, a first optical switch in which the input terminals of the first and second wavelength demultiplexers are respectively connected with its first and third output ports, the second working optical path is connected with its second output port, the second protection optical path is connected with its fourth output port, the output terminals of the first and second optical couplers are respectively connected with its second and fourth input ports, the first working optical path is connected with its first input port, and the first protection optical path is connected with its third input port, a second optical switch in which the input terminals of the third and fourth wavelength demultiplexers are respectively connected with its second and fourth output ports, the first working optical path is connected with its first output port, the first protection optical path is connected with its third output port, the output terminals of the third and fourth optical couplers are respectively connected with its first and third input ports, the second working optical path is connected with its second input port, and the second protection optical path is connected with its fourth input port, and a third optical switch in which the output terminals of the first to fourth wavelength demultiplexers are connected with its input ports and the input terminals of the first to fourth optical signal multiplexers are connected with its output ports.
At least one of the plural optical communication nodes forming the optical transmission apparatus further comprises a fourth optical switch in which its input ports are connected with the second output ports of the plural 2-input optical switches and its output ports are connected with the second input ports of the plural 2-input optical switches, a receiving means in which its reception signal input terminal is connected with the output ports of the fourth optical switch and which converts a reception optical signal inputted through the reception signal input terminal into an electrical signal, and a transmitting means in which its transmission signal output terminal is connected with the input ports of the fourth optical switch and which converts an electrical signal into an optical signal and outputs the transmission optical signal through the transmission signal output terminal.
A transmission apparatus failure recovering method according to the present invention comprises a process of detecting that a second working system optical transmission path and a first working system optical transmission path have become untransmissible between the two optical communication nodes being adjacent to each other which are used in the optical transmission apparatus, and a process of changing over the internal connections to the first input port and the second output port respectively to the third input port and the fourth output port in the first optical switch, and changing over the internal connections to the first output port and the second input port respectively to the third output port and the fourth input port in the second optical switch with regard to the internal connection state of an optical switch being closer to the untransmissible failure point out of the first and second optical switches contained in the two optical communication nodes, in case of detecting that they have become untransmissible.
A transmission apparatus failure recovering method according to the present invention comprises a process of detecting that all optical transmission paths have become untransmissible between the two optical communication nodes being adjacent to each other, and a process of changing over the internal connections to the first input port and the second output port respectively to the fourth input port and the third output port in the first optical switch, and changing over the internal connections to the first output port and the second input port respectively to the fourth output port and the third input port in the second optical switch with regard to the internal connection state of an optical switch being closer to the untransmissible failure point out of the first and second optical switches contained in the two optical communication nodes, in case of detecting that they have become untransmissible.
According to the present invention, plural cross-connecting circuits which have been provided for coping with such a failure of a transmission path as break of an optical fiber or the like in a structure according to the first prior art can be substituted with only the first and second optical path switching means provided in each optical communication node. Therefore, the apparatus can be made small-sized and economical. Furthermore, a structure being independent of the bit rate of a transmitted optical signal can be used thanks to replacing the cross-connecting circuits with the optical path switching means each being an optical circuit.
And according to the present invention, since each node switches over and introduces only optical signals to be dropped with an optical switch to a high-speed signal reception interface and passes signals to be passed through the node leaving as they are optical signals, it is possible to reduce the number of necessary high-speed signal transmission/reception interfaces and from this point also it is possible to reduce the cost.
And in the present invention, a 2-input switch contained in a third optical path switching means in each optical communication node performs connection of a main signal to a working optical path or connection of a main signal to a protection system transmission path. An optical transmission apparatus can be arbitrarily connected with any of the working system and the protection system through this 2-input optical switch. The optical transmission apparatus connected with the protection system transmits information other than information transmitted by the working system, namely, makes it possible to perform a communication called xe2x80x9cStandby-Line-Accesxe2x80x9d at an ordinary time when no failure occurs on the transmission path, and the transmission capacity of the system can be doubled.
Moreover, the present invention provides the fourth optical path switching means between the third optical path switching means and a receiving means, and between the third optical path switching means and a transmitting means. This fourth optical path switching means improves the degree of freedom of connection (rerouting) of the optical transmission apparatus and a ring-shaped optical transmission path, and facilitates a path setting operation in a large-scale node.